Prime Minister Manmohan Singh on Saturday embarked on a visit to the US to attend the Nuclear Security Summit where he is expected to pitch for firm response to the challenges of proliferation and possibility of terrorists gaining access to nuclear material. During the eight-day visit,Singh will also travel to Brazil to attend the Brazil-Russia-India-China (BRIC) and India-Brazil-South Africa (IBSA) Summits,where Iran's controversial nuclear programme and the impending UN sanctions would be among the key issues of discussions. In the first leg of the tour,Singh will be in Washington for four days during which he will attend the two-day Nuclear Security Summit on April 12 and 13 and meet US President Barack Obama and some other world leaders. The Summit,an initiative of Obama,will focus on dangers posed by clandestine proliferation and illicit trafficking of nuclear material and the possibility of terrorists acquiring atomic material. Singh is expected to share India's apprehensions about terrorists acquiring weapons of mass destruction. The threat is greater in Pakistan,where nuclear material is believed to be not too safe. Ahead of his visit,the Prime Minister said nuclear terrorism and proliferation of sensitive technologies are "legitimate concerns" which require "firm responses". He emphasised the need for "highest standards of security" in the nuclear field to reinforce public faith in the benefit of atomic science. "India welcomes President Obama's initiative to hold a Summit on Nuclear Security," said Singh,who will join leaders of 42 other countries in discussing ways to strengthen global initiatives for securing nuclear material and installations amid concerns of terrorists gaining access to these. Singh said he expected the Summit to focus on nuclear terrorism and proliferation of sensitive nuclear materials and technologies. "These are legitimate concerns which require firm responses," the Prime Minister said. Noting that nuclear energy was poised to play a growing role in addressing the developmental challenges of the present times,he said,"This will be possible only if we,as individual nations,and as a global community ensure the highest standards of security which reinforce public faith in the benefits of nuclear science." He pointed out that India was an important stakeholder in this global endeavour. Talking about India's well developed and indigenous nuclear energy programme,which dates back six decades,Singh said,"We have an impeccable record of security,safety and non-proliferation which reflects in our conduct as a responsible nuclear power."